Fuel pumping systems for aircraft which embody a redundant pump are known in the prior art. One type of pumping system incorporates two positive displacement pumping units driven by a common driving means but independently operable in the event of failure of one of the pumping units. This type of pumping system is shown in U.S. Pat. No. 3,008,426. A second type of pumping system incorporates a remotely mounted backup pump having its own drive means. An example of the second type of pumping system is disclosed in U.S. patent application No. 06/430,828 filed Sept. 30, 1982, entitled Tank Mounted Backup Fuel Pump.
Obviously, two drawbacks inherent in the first type of pumping system are that both pumping units are constantly running during operation and that performance must necessarily be affected with operation of only one pumping unit. The second type of pumping system suffers from complexity in that an alternate mounting arrangement and separate driving means are required.